Audible electrical telegraphy.



UNITED STATES PATENT OFFICE.

ROBERT OXLADE, OF REDFERN, NEAR SYDNEY, NEW SOUTH WALES, AUSTRALIA, ASSIGNOR OF TWO-FIFTHS TO WILLIAM JOSEPH WHITE RICHARDSON, OF PETERSHAM, NEAR SYDNEY, NEW SOUTH WALES,

AUSTRALIA.

1 AU DIBLE ELECTRICAL TELEG RAPHY.

SPECIFICATION forming part 01? Letters Patent NO. 721,084, dated February 17, 1903.

Application filed April 9. 1902. Serial No. 102,049. (No model.)

- To all whom it'may concern:

Be it known that 1, ROBERT OXLADE, electrical engineer, a subject of the King of Great Britain, residing at No. 177 George street, Redfern, near Sydney, in the State of New South Wales and Commonwealth of Australia, have invented new and useful Improvements in Audible Electric Telegraphy, of which the following is a specification.

The use of the relay on electric telegraphlines, specially on long ones, necessitates frequent hand adjustment due to such causes as loss of current on the line, and owing to the high resistance of the coils of the relays, especially of those employed on a long circuit, a large number of cells is required to force the current through the circuit. This involves a large annual'expenditure in any overland telegraph service for battery material alone, and in addition to this expense on the line-circuit it is necessary at most stations to use local batteries and instruments to complete the operation of making an audible sig nal. Heretofore it has been suggested that the telephone might be used instead of the ordinary telegraph instrument to receive ordinary Morse signals sent by a Morse key in the usual way; but it was soon found that the signals received in that way were not continually intelligible. After much experimenting I have arrived at the conclusion that when the telephone is used either on the closed-circuit method or on the opencircuit method the ear of an expert operator is now and then confused by the similarity of the sounds due to the make and to the break of the circuit and that this is fatal to the attempt to use the telephone instead of the register or sounder telegraph instrument for the purpose of receiving and yielding up andible signals, such as those sent by a Morse key in the usual ways. In these ways, either by the closed-circuit method or the open-circuit method, the signals are started on their course by the act of connecting the battery to the line or the making of metallic connection between the battery and the line, and the signals are read from the make or closing of circuit. Now by this improved system or method of audible electric telegraphy, which I call the induction system, the signals are made by breaking the, circuit, and they are recognized or read from the sounds produced by the break or opening of circuit, just the reverse of the method heretofore used. In this improved system, again, I do not connect the sending-battery to the line, but work the line by induced currents. Thus instead of employing a high electromotive force, such as a battery of thirty or more Daniells cells, to give the electric pressure needed to force a small current through a telegraphic line I employ a generator equal to, say, two such cells. According to this system the batterycurrent on the primary circuit is first stopped altogether and then started again as often as the sending-key breaks circuit at the contact-points, causing the lines of induction threaded through the coils of a transformer to collapse suddenly on breaking the circuit and to build up again on making the circuit. The induced difference of potential between the ends of the secondary winding of the transformer or induction-coil is much greater on breaking circuit in the primary than on making circuit in the primary. Therefore the sound yielded up by the telephone is greater for the break than the make.

an electrical engineer acquainted with the theory and mode of construction of transformers. I prefer to use a ratio of 2.5 to 1 or thereabout in winding our transformers to be used with a nearly-closed magnetic circuit and a ratio of about five to one for a mor fully open iron circuit.

The line-circuit on my system is either a closed metallic circuit or a single line of wire 9 connected to the earth at both ends in the usual way. A number of telegraph-stations can be connected to the same line by joining into the line the secondary winding of a transformer and a telephone-receiver in se- The actual value in volts of the induced difierence of ries, and each station being fitted with a complete set of the apparatus hereinafter described. I use a two-way switch to shortcircuit the secondary winding and to close the primary (battery) circuit in readiness for sending signals. By these means the resistance of the secondary coils used ata number of stations is removed from the line-circuit when those stations are ready to receive signals, and the battery or other generator in connection with the primary circuit is only put to work when a station is ready to send or is sending signals. The former operationnamely, short-circuiting the secondary coilis equivalent to removing from the line nearly all the inconvenient resistance of relays as used on an ordinary telegraph line. The telephone-receiver need not have a higher resistance than one hundred and twenty-five ohms, and if two receivers be used in parallel, as may be convenient, but no wise necessary except there he a number of stations,

the resistance would be only ohms. On

ordinary lines the number of battery-cells needed at each station to work my induction system would not exceed the number already used at telegraph-stations to work the local circuit for the sounder or register, and the large battery now used in telegraph services for sending current into the line would be dispensed with. The expensive relays and sounders of former systems are replaced by apparatus that costs little and needs no adjustments for variations of the current received from distant stations. Each station is independent so far as motive powerisconcerned. Again, by switching onto the primary circuit an ordinary microphone stations could use spoken words, when required, over long distances, and even without the addition of the microphone conversation could be carried on between adjacent stations through the telephone-receivers. A resonator may be used for the purpose of increasing the audible signals or Morse sounds on the telephone, and when this is so the receiver is placed inside it and connected to the line by means of flexible conductors. The resonator may be made of wood or glass or metal, the tone being different for each material. A lightning-arrester of ordinary telegraph pattern would be placed in the usual position at every station. The sending-key I use is an ordinary Morse key fitted with contact-points, as hereinafter described. When desirable, also, I connect a condenser across the terminals of the primary coil or else across the contacts of the key.

In my arrangement or installation I place a cell or other generator of low electromotive force in the primary circuit of a transformer or induction-coil, and by winding the transformer as hereinbefore explained and using the break of the primary circuit to start the signal I get the required pressure for operating the line and in this way force sufficient current through to cause an audible and dis tinct signal to be yielded up by a telephone. I divide this small battery, so that alternately the whole force of it or only a part of it will act through the said primary coil, or I have two independent small batteries connected so that alternately a current and then a comparatively weaker one will flow through said primary coil.- This alternation of currents of diiferent strengths is brought about by the peculiar construction of the sending-key and its connections, hereinafter described, with a primarycoil. Bymeansof thiskeythebreaking of the stronger current is followed by the breaking of the weaker current, so that the resulting induced current impulses in the secondary winding of the transformer (which is in circuit between the communicating stations) and in the telephones are caused to be of two diiferent strengths. The first current impulse in the line from which the signal is read is due to the breaking of the stronger primary current, while the second current impulse, due to the breaking of the weaker primary current, signals the cessation of the first impulse, and the sound in the telephone due to the closing of the primary circuit is not heard as a separate sound during signaling. Thus the breaking of the primary circuit is completed twice for each separate signalthat is, twice for each separate letter or each separate part of a letter or figure signaled on the induction line-wire-with the result that sounds transmitted and received are identical with those on the well-known Morse sounder as ordinarily used. This installation also works Well with a condenser inserted in the line (induced-current) circuit when the line is of small resistance.

In order that this invention maybe clearly understood, reference will now be made to the drawings, in Which- Fignre 1 is a diagram of an installation of electrical parts or integers for the carrying into effect of my improvements arranged as in a terminal station, while Fig. 2 is a side elevation of the sending-key.

The primary circuit is shown by full lines a, a, and a", while the secondary circuit is shown by dotted lines I) and b A is a telephone-receiver shown without a resonator.

B is the transformer or induction-coil; O, a two-wayswitch; D, a battery, and E the sending-key.

Signaling being received, the secondary winding of the transformers B is short-circuited through line b and contact 0 and the arm O of the switch C making contact with the post C. When the switch is turned to close the primary circuit to prepare to send signals, arm O takes on contacts 0, and the current on the primary circuit flows from battery D along line a to the metallic bridge E and through the contact-point E supported by the bridge, along the arm E of the key to the binding-post E and thence along line a to post C, thence along the arm O to con- IIO tact C to the terminal B of the primary winding, through the primary winding to terminal B and thence to battery D. When the sending-key is being depressed, the primary circuit is broken between the contact-point E supported by the bridge Efiand the arm E of the key, and at that moment an induced current flows from the secondary winding of transformer B to terminal A thence to the line b, and returns either through the earth F or else through another line wire and through the telephone A, rentering transformer B at the terminal A or the induced current may flow in the opposite direction, starting from terminal A and rentering at terminal A When the arm of the sending-key is depressed onto the bottom front contact-stop E the primary circuit is at once closed again, and the primary current flows from part X of the battery D (or from a smaller battery) along line a, to contact E thence into the arm E of the key to the post E and along line a to post 0 thencealong the arm O of the switch 0 to contact 0, thence to terminal B and through the primary winding to terminal B and thence to the smaller battery or part D, so using the magnetizing-current of one cell. When the arm of the key is rising from contact E the pri mary circuit is again broken and an induced current flows along the line-circuit; but it is of smaller magnitude than before. When the arm of the key has finished its upward stroke, the primary circuit is again energized by the whole battery.

Having now particularly described and as: certained the nature ofmy said invention and in What manner the same is to be performed, I declare that what I claim is' 1. In a telegraphic system, the combination with the line, of a receiving device connected thereto, a transformer therein, a source of current connected to the primary coil of said transformer, a key included between the source of current and the transformer,,whereby current impulses of alternately-different strength may be sent to the transformer and thereby send similar induced currents to line,

and means to short-circuit the transformer point, whereby the whole current will beclosed through the primary coil of the transformer when the key contacts with one of the points and part of the current be closed therethrough when the key contacts with the other point, substantially as described.

3. In a telegraphic system, the combination with the line-wire, of a transformer and a grounded telephone connected in series therewith, a sending key having two contactpoints, a plurality of battery-cells included between one of the contact-points and the primary coil of the transformer, means to short-circuit the transformer and connect the telephone directly to line, a shunt connecting less than the whole number of battery-cells to the second contact-point of the key, whereby currents of different strength are alternately sent through the primary coil of the transformer to send similar induced currents to line, substantially as described.

4. In a telegraph system, the combination with the line, a transformer having its secondary coil in series therewith, a sending-key to close primary circuits of difierent strength through the primary Winding of said transformer, a grounded telephone connected in series with the secondary winding of the transformer and a shunt to-the telephone, whereby the transformer may be cut out of circuit when receiving messages, substantially as described. r

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

ROBERT OXLADE.

Witnesses FRED WALSH, PERCY NEWELL. 

